Forward

Scientists studying ecosystem–atmosphere interactions require networks of micrometeorological instruments to measure the fluxes of carbon dioxide, water and energy across a spectrum of biomes and climate zones. For example, a global network of flux measurement sites, called FLUXNET, has the potential to act as a ‘canary in the mine’ with regards to quantifying how the terrestrial biosphere's metabolism is responding to global change (e.g., warming, elevated CO2, air pollution, disturbance and land use change). At present, carbon dioxide and water vapour fluxes are being measured continuously at over 300 research sites world-wide. Individual research sites in this dispersed network are funded by and are operated through the auspices of regional networks in North America (AmeriFlux, http://public.ornl.gov/ameriflux/; Fluxnet-Canada; http://www.fluxnet-canada.ca/), South America (LBA), Europe (CarboEuroFlux; http://www.carboeurope.org/), Australasia (OzFlux; http://www.dar.csiro.au/lai/ozflux/), Asia (China Flux; http://www.chinaflux.org/), and Asia Flux; (http://www-cger2.nies.go.jp/asiaflux/index.html) and Africa (AfriFlux). In December 2004 we convened an international FLUXNET workshop in Firenze, Italy. One goal of the workshop was to produce an update of the progress made over the past 10 years of the network's existence; the network was launched in March, 1995, when a group of scientists met at La Thuile, Italy, drafted a plan, and presented a series of papers that culminated in a special issue of Global Change Biology, published in 1996 (Vol. 2, Issue 3). Other goals of the workshop, and the focus of this special issue, were to examine issues relating to the inter-annual variability of carbon fluxes and to extend datasets to user communities such as ecology, global climate change modelling and biogeochemistry. In this special issue of Global Change Biology, articles by Dunn et al. and Barr et al. examine the magnitudes and processes contributing to the inter-annual variability of carbon fluxes using data from a regional network of sites in Canada. An analysis by Wang et al. uses flux data from a range of plant functional types and climate zones to compute, via inversion, model parameters for canopy photosynthesis. They then examine the seasonality of these parameters. Enquist et al. uses flux data from the network to examine ecological scaling theory. Regional-scale analyses are produced by Miglietta et al. and Reichstein et al. Miglietta et al. combined measurements from an instrumented aircraft and a tower network to look at fluxes over a 21-day period around the Netherlands, while Reichstein et al. used the CarboEuroFlux network, and satellite measurements and models, to examine carbon flux anomalies during the 2003 heat spell and drought across Europe. Finally, Friend et al. used the data to validate, calibrate and parameterize land surface algorithms that are used in a new generation of coupled carbon – climate models.